Cathode mounting for mercury vapor devices



\ K. BRABAND CATHODE MOUNTING FOR MERCURY VAPOR DEVICES Filed Dec. 10. 19:50

Jul 26, 1932.

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Inventor! Karl Brabcmd,

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\ cury condensed on the wall of Patented July 26, 1932 M UNITED STATES PATENT KARL BRAZBAND, or BERLIN, GEBMANY, ASSIGNOR T0 GENERAL ELECTRIC COMPANY,

A CORPORATION on NEW YORK I V CATHODE MOUNTING FOR MERCURY VAPOR DEVICES Application filed December 10. 1930, Serial No. 501,408, and in Germany December 9, 1929.

My invention relates to are discharge apparatus such as mercury arc rectifiers,,particularly to cathode systems for such apparatus, and has for its principal object the provision of an improved cathode arrangement wherein the cathode container is elfec tively supported and insulated by simple means.

In mercury vapor rectifiers and similar apparatus in which the evacuated containing vessel is of metal, the cathode must be insulated from the wall of the vessel. Otherwise, even though an annular insulator were arranged on the inside of the vessel in such a way that a cathode spot from the cathode container could reach the metal wall of the vessel only by passing over this insulator, nevertheless cathode spots would very' frequently arise on the numerous drops of merthe vessel. This difiiculty has been obviated hitherto either by the use of an annular insulator for the cathode container, this insulator at the same time forming a part of the evacuated vessel wall; or by the use of a cathode container composed of insulating material and having a current lead-in arranged above the cathode; or finally, by the use of a metallic container insulated from the evacuated vessel.

In the first case above cited, the sealing of the cathode structure introduces serious difii culties, particularly in case of cathods of large diameter. It has not been found possible to provide insulators for this purpose which are directly fused to the evacuated vessel and to the current conductor, so that only seals which are not subject to change by heat and which include intermediate layers of elastic material can be used.

In the second case cited, the large mercury-filled container formed of insulating material does not well withstand mechanical shocks and stresses in transit. Further, the leading in of the current from above the cathode in the case of mercury are devices carrying large currents is uiisuitablebecause of the resulting electro-dynamicextension of the arc path. 9 v

In the third case cited an accumulation tallic evacuated vessel of the rectifier. To T avoid this difficulty either the walls ofjthe evacuated vessel in the vicinity of the oathode container must be heated or thecathode must be efiectively cooled.

The present invention relates to a cathode arrangement which avoids the disadvantages existing in arrangements well known hitherto. In accordance with the invention these disadvantages are avoided by the provision of a metallic container for the mercury cathode which is supported by a vacuum-tight insulator for the lead-in conductor to the cathode, this insulator being arranged at the bottom of the rectifier evacuated vessel. By means of an intermediate insulating mem ber the cathode container is sealed off from the vapor chamber above the cathode in such a way that mercury does not pass into the space intermediate the cathode container and the bottom of the evacuated vessel. For evacuating this intermediate space there may be provided a connection, preferably tubular, between this space and a locality within the rectifier vessel in which the mean mercury vapor pressure is lower than the saturation pressure of the mercury vapor at the mean temperature of this intermediate space.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, the single figure thereof illustrates diagrammatically an arc discharge device in which my invention has been embodied.

.In the figure is shown an arc discharge device such as a mercury vapor rectifier comprising a metallic cathode container 1 having mercury 2 therein and arranged in the lower part of a metallic tank or evacuated vessel 8 in which are mounted anodes 4 and 5. The current connection to the cathode is effected by'means of the currentconductor 6 sealed fromthe wall 7 of the evacuated 100 vessel 3 by the lead-in insulator 8 which is of smaller diameter than that of the cathode container 1. The intermediate space 9 between this container and the wall of the evacuated vessel 3 is sealed from the vapor chamber portion 10 of the evacuated vessel by means of an annular insulator 11 mounted between the cathode container 1 and a ring the saturation pressure of mercury vapor at the mean temperature or" intermediate space 9, cooling means in the vessel 3 comprising a double-walled annular member 15 may be provided, the walls of this member being cooled by any well known suitable means.

In order to simplify the mounting'and sealing of the annular insulator 11, between the, cathode container 1 and the ring 12 of the evacuated vessel 3, the bottom portion 16 of'the vessel wall 7 is made rigid through out its central portion through which passes the conductor 6 and insulator 8 but at its edge 17 is formed likea diaphragm, to pro vide a degree of elasticity. Therefore the external atmospheric pressure on the bottom wall portion 16, acting through the insula-e tor 8 and current conductor 6, presses the cathode container 1 against the annular insulator 11 and the latter against the ring12, and the usual screws for the assembly of the container 1 and insulator 11 to the wall 7 of the evacuated vessel are unnecessary.

To remove small quantities of mercury which might possibly pass through the joints between the ring 12 and insulator 11 and between the latter and cathode container 1 into the intermediate space 9, this space may be heated by any suitable, means, or, for the removal of the mercury from space 9 a collecting tube 18 maybe mounted on thebottom portion of the vessel wall 7 and provided with a heating winding 19. r The mercury 20 collecting in tube 18 is heated to the evaporation point by means of the winding 19 and the vapor escapes through a conduit, as tube 21, which passes flOIl'l'llhG tube 18 to a point .within the vessel 3 adjacent a cooled surface, as surface 22. The condensate does not return to the intermediate space 9 but flows back, to the cathode container 1.

,VV hat I claim as new and desire tosecure by Letters Patent of the United States, is:

1. In an arc discharge device comprising a metallic evacuated vessel and a mercury cathode therein, means forming a vapor chamber within said vessel above said cathode therein, means forming a vapor chamber within said vessel above said cathode, a metallic container for said cathode, a current conductor connected to said container, an insulator associated with said conductor, said insulator being mounted in the bottom ofsaid vesselto support said cathode container, said container and a portion of the wall of said vessel forming a space within said, vessel below said container, means to seal andinsulate said container from said vapor chamber, and

a conduit connecting said space to a locality in said vapor chamber in which the mean vapor pressure is lower than the mean saturation pressure of the vapor in saidspace below said cathode container.

3. In an arc discharge device comprising an evacuated vessel and, a mercury cathode therein, a container for said cathode, means associated with said vessel to support said container above the bottom of said vessel, said container and a portion of the wall of said vessel forming a sealed space within said vessel below said container, said vessel having at one locality thereof a vapor pres.- sure lower than the mean'saturation pressure of the vaporin said space below saidc0ntainer, and means to connect said space and said locality of lower vapor pressure.

4:. In an arc discharge device comprising an evacuated vessel and a mercury cathode therein, means forming a vapor chamber within said vessel above said cathode, said vessel including a diaphragm having a rigid central portion and an annular elastic portion, a container for said cathode, means to seal said container from said vapor chamber, and means associated with said diaphragm to support said container, whereby the external atmospheric pressure on said diaphragm is transmitted to said container to press said container against the'lower edge of saidvapor chamber. V V i 5. In an arc discharge device comprising an evacuated vessel and a mercury cathode therein, a container for said cathode, means associated with said vessel to support said container above the bottom of said vessel,

said container and a portion of the wall of said vessel forming a sealed space within said vesselbelow said container, a mercury col lecting chamber in communication with said sealed space, means to heat the mercury collected within said chamber, condensation means associated with said vessel outside said sealed space, and means to conduct vapor from said chamber to a point in said vessel adjacent said condensation means.

In Witness whereof, I have hereunto set my hand this 29th day of November, 1930.

KARL BRABAND. 

